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<title>Picocli 2.0: Groovy Scripts on Steroids</title>
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<body class="article">
<div id="header">
<h1>Picocli 2.0: Groovy Scripts on Steroids</h1>
</div>
<div id="content">
<div id="preamble">
<div class="sectionbody">
<div class="paragraph">
<p>Picocli 2.0 adds improved support for other JVM languages, especially Groovy.
Why use picocli when the Groovy language has built-in CLI support with the <a href="http://docs.groovy-lang.org/2.4.7/html/gapi/groovy/util/CliBuilder.html">CliBuilder</a> class?</p>
</div>
<div class="paragraph">
<p>You may like picocli&#8217;s usage help, which shows ANSI <a href="http://picocli.info/#_ansi_colors_and_styles">colors and styles</a>
by default. Another feature you may fancy is the command line
<a href="http://picocli.info/autocomplete.html">TAB autocompletion</a>. Finally, there is a slew of smaller features,
like the fact that your script needs zero lines of command line parsing code,
picocli&#8217;s <a href="http://picocli.info/#_subcommands">subcommand</a> support,
<a href="http://picocli.info/#_strongly_typed_everything">type conversion</a> for both options and positional parameters,
and <a href="http://picocli.info/#_tracing">parser tracing</a>, to name a few.</p>
</div>
<div class="paragraph text-center">
<p><span class="image"><img src="images/cli.jpg" alt="cli" width="20%"></span></p>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_example">Example</h2>
<div class="sectionbody">
<div class="paragraph">
<p>Let&#8217;s take a look at an example. The <code>checksum.groovy</code> script below takes one or more file parameters,
and for each file prints out a checksum and the file name. The "checksum" algorithm is MD5 by default,
but users may specify a different MessageDigest algorithm. Users can request usage help with the
<code>-h</code> or <code>--help</code> option.</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="CodeRay highlight nowrap"><code data-lang="groovy"><span class="annotation">@Grab</span>(<span class="string"><span class="delimiter">'</span><span class="content">info.picocli:picocli:2.0.3</span><span class="delimiter">'</span></span>)
<span class="annotation">@picocli</span>.groovy.PicocliScript
<span class="keyword">import</span> <span class="include">groovy.transform.Field</span>
<span class="keyword">import</span> <span class="include">java.security.MessageDigest</span>
<span class="keyword">import</span> <span class="include">static</span> <span class="include">picocli.CommandLine.*</span>

<span class="annotation">@Parameters</span>(arity=<span class="string"><span class="delimiter">&quot;</span><span class="content">1</span><span class="delimiter">&quot;</span></span>, paramLabel=<span class="string"><span class="delimiter">&quot;</span><span class="content">FILE</span><span class="delimiter">&quot;</span></span>, description=<span class="string"><span class="delimiter">&quot;</span><span class="content">The file(s) whose checksum to calculate.</span><span class="delimiter">&quot;</span></span>)
<span class="annotation">@Field</span> <span class="predefined-type">File</span><span class="type">[]</span> files

<span class="annotation">@Option</span>(names = [<span class="string"><span class="delimiter">&quot;</span><span class="content">-a</span><span class="delimiter">&quot;</span></span>, <span class="string"><span class="delimiter">&quot;</span><span class="content">--algorithm</span><span class="delimiter">&quot;</span></span>], description = [
        <span class="string"><span class="delimiter">&quot;</span><span class="content">MD2, MD5, SHA-1, SHA-256, SHA-384, SHA-512,</span><span class="delimiter">&quot;</span></span>,
        <span class="string"><span class="delimiter">&quot;</span><span class="content">  or any other MessageDigest algorithm.</span><span class="delimiter">&quot;</span></span>])
<span class="annotation">@Field</span> <span class="predefined-type">String</span> algorithm = <span class="string"><span class="delimiter">&quot;</span><span class="content">MD5</span><span class="delimiter">&quot;</span></span>

<span class="annotation">@Option</span>(names= [<span class="string"><span class="delimiter">&quot;</span><span class="content">-h</span><span class="delimiter">&quot;</span></span>, <span class="string"><span class="delimiter">&quot;</span><span class="content">--help</span><span class="delimiter">&quot;</span></span>], usageHelp= <span class="predefined-constant">true</span>, description= <span class="string"><span class="delimiter">&quot;</span><span class="content">Show this help message and exit.</span><span class="delimiter">&quot;</span></span>)
<span class="annotation">@Field</span> <span class="type">boolean</span> helpRequested

files.each {
  println <span class="predefined-type">MessageDigest</span>.getInstance(algorithm).digest(<span class="local-variable">it</span>.bytes).encodeHex().toString() + <span class="string"><span class="delimiter">&quot;</span><span class="char">\t</span><span class="delimiter">&quot;</span></span> + <span class="local-variable">it</span>
}</code></pre>
</div>
</div>
<div class="paragraph">
<p>When run in the <code>$picocli-home/examples/src/main/groovy/picocli/examples</code> directory,
this example script gives the following results:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="CodeRay highlight nowrap"><code data-lang="bash">$ groovy checksum.groovy *.*
4995d24bbb3adf67e2120c36dd3027b7        checksum.groovy
a03c852de017f9303fcc373c7adafac6        checksum-with-banner.groovy
1ee567193bf41cc835ce76b6ca29ed30        checksum-without-base.groovy</code></pre>
</div>
</div>
<div class="paragraph">
<p>Invoking the script with the <code>-h</code> or <code>--help</code> option shows the usage help message
with ANSI colors and styles below:</p>
</div>
<div class="paragraph">
<p><span class="image"><img src="images/GroovyChecksum.png" alt="Usage help with ANSI colors and styles"></span></p>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_where_s_the_code">Where&#8217;s the Code?</h2>
<div class="sectionbody">
<div class="paragraph">
<p>You may have noticed that the above script does not contain any logic for parsing the command
line arguments or for handling requests for usage help.</p>
</div>
<div class="paragraph text-center">
<p><span class="image"><img src="images/WhereIsMyCode.png" alt="Dude" width="35%"></span></p>
</div>
<div class="paragraph">
<p>Without the <code>@picocli.groovy.PicocliScript</code> annotation, the script code would look something like this:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="CodeRay highlight nowrap"><code data-lang="groovy"><span class="type">class</span> <span class="class">Checksum</span> {
    <span class="annotation">@Parameters</span>(arity = <span class="string"><span class="delimiter">&quot;</span><span class="content">1</span><span class="delimiter">&quot;</span></span>, paramLabel = <span class="string"><span class="delimiter">&quot;</span><span class="content">FILE</span><span class="delimiter">&quot;</span></span>, description = <span class="string"><span class="delimiter">&quot;</span><span class="content">...</span><span class="delimiter">&quot;</span></span>)
    <span class="predefined-type">File</span><span class="type">[]</span> files

    <span class="annotation">@Option</span>(names = [<span class="string"><span class="delimiter">&quot;</span><span class="content">-a</span><span class="delimiter">&quot;</span></span>, <span class="string"><span class="delimiter">&quot;</span><span class="content">--algorithm</span><span class="delimiter">&quot;</span></span>], description = [<span class="string"><span class="delimiter">&quot;</span><span class="content">...</span><span class="delimiter">&quot;</span></span>])
    <span class="predefined-type">String</span> algorithm = <span class="string"><span class="delimiter">&quot;</span><span class="content">MD5</span><span class="delimiter">&quot;</span></span>

    <span class="annotation">@Option</span>(names = [<span class="string"><span class="delimiter">&quot;</span><span class="content">-h</span><span class="delimiter">&quot;</span></span>, <span class="string"><span class="delimiter">&quot;</span><span class="content">--help</span><span class="delimiter">&quot;</span></span>], usageHelp = <span class="predefined-constant">true</span>, description = <span class="string"><span class="delimiter">&quot;</span><span class="content">...</span><span class="delimiter">&quot;</span></span>)
    <span class="type">boolean</span> helpRequested
}
<span class="predefined-type">Checksum</span> checksum = <span class="keyword">new</span> <span class="predefined-type">Checksum</span>()
CommandLine commandLine = <span class="keyword">new</span> CommandLine(checksum)
<span class="keyword">try</span> {
    commandLine.parse(args)
    <span class="keyword">if</span> (commandLine.usageHelpRequested) {
        commandLine.usage(<span class="predefined-type">System</span>.out)
    } <span class="keyword">else</span> {
        checksum.files.each {
            <span class="type">byte</span><span class="type">[]</span> digest = <span class="predefined-type">MessageDigest</span>.getInstance(checksum.algorithm).digest(<span class="local-variable">it</span>.bytes)
            println digest.encodeHex().toString() + <span class="string"><span class="delimiter">&quot;</span><span class="char">\t</span><span class="delimiter">&quot;</span></span> + <span class="local-variable">it</span>
        }
    }
} <span class="keyword">catch</span> (ParameterException ex) {
    println ex.message
    commandLine.usage(<span class="predefined-type">System</span>.out)
}</code></pre>
</div>
</div>
<div class="paragraph">
<p>The above example has explicit code to parse the command line, deal with invalid user input,
and check for usage help requests.
The first version of the script did not have any of this boilerplate code.</p>
</div>
<div class="paragraph">
<p>Let&#8217;s take a look at how this works.</p>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_basescript">Basescript</h2>
<div class="sectionbody">
<div class="paragraph">
<p>Scripts annotated with <code>@picocli.groovy.PicocliScript</code> are automatically transformed to use
<code>picocli.groovy.PicocliBaseScript</code> as their base class.
This turns a Groovy script into a picocli-based command line application.</p>
</div>
<div class="paragraph text-center">
<p><span class="image"><img src="images/AllYourBase.png" alt="AllYourBase" width="35%"></span></p>
</div>
<div class="paragraph">
<p>When the script is run, Groovy calls the script&#8217;s <code>run</code> method.
The <code>PicocliBaseScript::run</code> method takes care of parsing the command line and populating the script
fields with the results. The run method does the following:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>First, <code>@Field</code> variables annotated with <code>@Option</code> or <code>@Parameters</code> are initialized from the command line arguments.</p>
</li>
<li>
<p>If the user input was invalid, an error message is printed followed by the usage help message.</p>
</li>
<li>
<p>If the user requested usage help or version information, this is printed to the console and the script exits.</p>
</li>
<li>
<p>Otherwise, the script body is executed.</p>
</li>
</ul>
</div>
<div class="paragraph">
<p>This behavior can be customized, see the <a href="http://picocli.info/apidocs/picocli/groovy/PicocliBaseScript.html#run--">PicocliBaseScript javadoc</a> for more details.</p>
</div>
<div class="paragraph">
<p>In addition to changing the script base class, the <code>@PicocliScript</code> annotation also allows Groovy
scripts to use the <code>@Command</code> annotation directly, without introducing a helper class.
The picocli parser will look for this annotation on the
class containing the <code>@Option</code> and <code>@Parameters</code>-annotated fields. The same custom
<a href="http://picocli.info/apidocs/picocli/groovy/PicocliScriptASTTransformation.html">AST transformation</a>
that changes the script&#8217;s base class also moves any <code>@Command</code> annotation in the script to this
transformed class so the picocli parser can pick it up.</p>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_usage_help_with_colors">Usage Help With Colors</h2>
<div class="sectionbody">
<div class="paragraph">
<p>The <code>@Command</code> annotation lets you customize parts of the <a href="http://picocli.info/#_usage_help">usage help</a> message like command name, description, headers, footers etc.</p>
</div>
<div class="paragraph">
<p>Let&#8217;s add some bells and whistles to the example script.
(Credit to <a href="http://patorjk.com/software/taag/" class="bare">http://patorjk.com/software/taag/</a> for the ASCII Art Generator.)</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="CodeRay highlight nowrap"><code data-lang="groovy"><span class="annotation">@Grab</span>(<span class="string"><span class="delimiter">'</span><span class="content">info.picocli:picocli:2.0.3</span><span class="delimiter">'</span></span>)
<span class="annotation">@Command</span>(header = [
        <span class="error">$</span><span class="regexp"><span class="delimiter">/</span><span class="content">@|bold,green    ___                            ___ _           _                  |@</span><span class="delimiter">/</span></span><span class="error">$</span>,
        <span class="error">$</span><span class="regexp"><span class="delimiter">/</span><span class="content">@|bold,green   </span><span class="delimiter">/</span></span> __|_ _ ___  _____ ___  _     / __| |_  ___ __| |__ ____  _ _ __  |<span class="error">@</span><span class="regexp"><span class="delimiter">/</span><span class="content">$</span><span class="content">,</span></span><span class="error">
</span>        <span class="error">$</span>/<span class="error">@</span>|bold,green  | (_ | <span class="string"><span class="delimiter">'</span><span class="content">_/ _ \/ _ \ V / || |   | (__| </span><span class="delimiter">'</span></span> <span class="error">\</span>/ -_) _| <span class="regexp"><span class="delimiter">/</span><span class="content"> </span><span class="delimiter">/</span></span>(_-&lt; || | <span class="string"><span class="delimiter">'</span><span class="content">  \ |@/$,</span></span><span class="error">
</span>        <span class="error">$</span>/<span class="error">@</span>|bold,green   <span class="error">\</span>___|_| <span class="error">\</span>___/<span class="error">\</span>___/<span class="error">\</span>_/ <span class="error">\</span>_, |    <span class="error">\</span>___|_||_<span class="error">\</span>___<span class="error">\</span>__|_<span class="error">\</span>_<span class="error">\</span>/__/<span class="error">\</span>_,_|_|_|_||<span class="error">@</span><span class="regexp"><span class="delimiter">/</span><span class="content">$</span><span class="content">,</span></span><span class="error">
</span>        <span class="error">$</span>/<span class="error">@</span>|bold,green                         |__/                                         |<span class="error">@</span><span class="regexp"><span class="delimiter">/</span><span class="content">$</span></span><span class="error">
</span>        ],
        description = <span class="string"><span class="delimiter">&quot;</span><span class="content">Print a checksum of each specified FILE.</span><span class="delimiter">&quot;</span></span>,
        version = <span class="string"><span class="delimiter">'</span><span class="content">checksum v1.2.3</span><span class="delimiter">'</span></span>, showDefaultValues = <span class="predefined-constant">true</span>,
        footerHeading = <span class="string"><span class="delimiter">&quot;</span><span class="content">%nFor more details, see:%n</span><span class="delimiter">&quot;</span></span>,
        footer = [<span class="string"><span class="delimiter">&quot;</span><span class="content">[1] https://docs.oracle.com/javase/9/docs/specs/security/standard-names.html</span><span class="delimiter">&quot;</span></span>,
                <span class="string"><span class="delimiter">&quot;</span><span class="content">ASCII Art thanks to http://patorjk.com/software/taag/</span><span class="delimiter">&quot;</span></span>]
)
<span class="annotation">@picocli</span>.groovy.PicocliScript
<span class="keyword">import</span> <span class="include">groovy.transform.Field</span>
<span class="keyword">import</span> <span class="include">java.security.MessageDigest</span>
<span class="keyword">import</span> <span class="include">static</span> <span class="include">picocli.CommandLine.*</span>

<span class="annotation">@Parameters</span>(arity=<span class="string"><span class="delimiter">&quot;</span><span class="content">1</span><span class="delimiter">&quot;</span></span>, paramLabel=<span class="string"><span class="delimiter">&quot;</span><span class="content">FILE</span><span class="delimiter">&quot;</span></span>, description=<span class="string"><span class="delimiter">&quot;</span><span class="content">The file(s) whose checksum to calculate.</span><span class="delimiter">&quot;</span></span>)
<span class="annotation">@Field</span> <span class="directive">private</span> <span class="predefined-type">File</span><span class="type">[]</span> files

<span class="annotation">@Option</span>(names = [<span class="string"><span class="delimiter">&quot;</span><span class="content">-a</span><span class="delimiter">&quot;</span></span>, <span class="string"><span class="delimiter">&quot;</span><span class="content">--algorithm</span><span class="delimiter">&quot;</span></span>], description = [
        <span class="string"><span class="delimiter">&quot;</span><span class="content">MD2, MD5, SHA-1, SHA-256, SHA-384, SHA-512, or</span><span class="delimiter">&quot;</span></span>,
        <span class="string"><span class="delimiter">&quot;</span><span class="content">  any other MessageDigest algorithm. See [1] for more details.</span><span class="delimiter">&quot;</span></span>])
<span class="annotation">@Field</span> <span class="directive">private</span> <span class="predefined-type">String</span> algorithm = <span class="string"><span class="delimiter">&quot;</span><span class="content">MD5</span><span class="delimiter">&quot;</span></span>

<span class="annotation">@Option</span>(names= [<span class="string"><span class="delimiter">&quot;</span><span class="content">-h</span><span class="delimiter">&quot;</span></span>, <span class="string"><span class="delimiter">&quot;</span><span class="content">--help</span><span class="delimiter">&quot;</span></span>], usageHelp=<span class="predefined-constant">true</span>, description=<span class="string"><span class="delimiter">&quot;</span><span class="content">Show this help message and exit.</span><span class="delimiter">&quot;</span></span>)
<span class="annotation">@Field</span> <span class="directive">private</span> <span class="type">boolean</span> helpRequested

<span class="annotation">@Option</span>(names= [<span class="string"><span class="delimiter">&quot;</span><span class="content">-V</span><span class="delimiter">&quot;</span></span>, <span class="string"><span class="delimiter">&quot;</span><span class="content">--version</span><span class="delimiter">&quot;</span></span>], versionHelp=<span class="predefined-constant">true</span>, description=<span class="string"><span class="delimiter">&quot;</span><span class="content">Show version info and exit.</span><span class="delimiter">&quot;</span></span>)
<span class="annotation">@Field</span> <span class="directive">private</span> <span class="type">boolean</span> versionInfoRequested

files.each {
  println <span class="predefined-type">MessageDigest</span>.getInstance(algorithm).digest(<span class="local-variable">it</span>.bytes).encodeHex().toString() + <span class="string"><span class="delimiter">&quot;</span><span class="char">\t</span><span class="delimiter">&quot;</span></span> + <span class="local-variable">it</span>
}</code></pre>
</div>
</div>
<div class="paragraph">
<p>The new version of the script adds a header and footer, and the ability to print version information.
All text displayed in the usage help message and version information may contain format specifiers
like the <code>%n</code> line separator.</p>
</div>
<div class="paragraph">
<p>The usage help message can also display ANSI colors and styles.
Picocli supports a simple markup syntax where <code>@|</code> starts an ANSI styled section and <code>|@</code> ends it.
Immediately following the <code>@|</code> is a comma-separated list of colors and styles,
like <code>@|STYLE1[,STYLE2]&#8230;&#8203; text|@</code>.
See the picocli <a href="http://picocli.info/#_usage_help_with_styles_and_colors">user manual</a> for details on what colors and styles are available.</p>
</div>
<div class="paragraph">
<p>The usage help message for the new script looks like this:</p>
</div>
<div class="paragraph">
<p><span class="image"><img src="images/GroovyChecksumWithBanner.png" alt="Customized header and footer with styles and colors"></span></p>
</div>
<div class="paragraph">
<p>The <code>@Command</code> annotation also has a <code>version = "checksum v1.2.3"</code> attribute.
This version string is printed when the user specifies <code>--version</code> on the command line because
we declared an <code>@Option</code> with that name with attribute <code>versionHelp = true</code>.</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="CodeRay highlight nowrap"><code data-lang="bash">$ groovy checksum-with-banner.groovy --version
checksum v1.2.3</code></pre>
</div>
</div>
<div class="paragraph">
<p>For more details, see the <a href="http://picocli.info/#_version_help">Version Help</a> section of the user manual.</p>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_conclusion">Conclusion</h2>
<div class="sectionbody">
<div class="paragraph">
<p>The <code>@PicocliScript</code> annotation allows Groovy scripts to omit boilerplate code and while adding powerful common command line application functionality.
In the final version of our example script, most of the code is actually description text for the usage help message.</p>
</div>
<div class="paragraph">
<p>There is a lot more to picocli, give it a try!</p>
</div>
<div class="paragraph">
<p>Please star the <a href="https://github.com/remkop/picocli">project on GitHub</a> if you like it and tell your friends!</p>
</div>
</div>
</div>
</div>
<div id="footer">
<div id="footer-text">
Last updated 2017-11-11 00:02:25 +09:00
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